The prior art dealing with catalytic cracking catalysts has in large part evolved by the preparation of modified zeolites for use as components in cracking catalysts. The following patents are representative of the prior art dealing with zeolites and matrices.
The use of conversion catalysts formed from a zeolite dispersed in a siliceous matrix has been disclosed in U.S. Pat. No. 3,140,249 and U.S. Pat. No. 3,352,796.
The use of blended matrix components, e.g., a catalyst comprising a zeolite, an inorganic oxide matrix and inert fines, which may be alpha alumina, is disclosed in U.S. Pat. No. 3,312,615. Catalysts comprising an amorphous silica-alumina, separately added alumina and a zeolite are disclosed in U.S. Pat. No. 3,542,670 and catalyst comprising a zeolite, an amorphous hydrous alumina and alumina monohydrate are disclosed in U.S. Pat. No. 3,428,550.
It has been disclosed that the steam and thermal stability of Y zeolites can be improved by the use of zeolites having a low level of alkali metal content and a unit cell size less than about 24.45 Angstroms (See: U.S. Pat. Nos. 3,293,192 and Re. 28,629 (Reissue of U.S. Pat. No. 3,402,996)).
Further, it has been disclosed (U.S. Pat. No. 3,591,488) that the hydrogen or ammonium form of a zeolite may be treated with H.sub.2 O at a temperature ranging from about 800.degree. to about 1500.degree. F., and then subsequently cation exchange the steam and water treated zeolite with cations which may be rare earth metal cations. U.S. Pat. No. 3,676,368 discloses a rare earth exchanged-hydrogen faujasite containing from 6 to 14 percent rare earth oxides. U.S. Pat. No. 3,957,623 discloses a rare earth exchanged zeolite having a total of 1 to 10 weight percent rare earth metal oxide. U.S. Pat. No. 3,607,043 discloses a process for preparing a zeolite having a rare earth content of 0.3 to 10 weight percent.
U.S. Pat. No. 4,036,739 discloses hydrothermally stable and ammonia stable Y zeolite in which a sodium Y zeolite is ion exchanged to partially exchange sodium ions for ammonium ions, followed by steam calcination and a further ion exchange with ammonium to reduce the final sodium oxide content to below 1 weight percent, followed by calcination of the reexchanged product, or according to U.S. Pat. No. 3,781,199, the second calcination may be conducted after the zeolite is admixed with a refractory oxide.
The products obtained by use of such aforementioned catalysts may not be the most desirable in all instances. Accordingly, catalysts and processes have been developed to modify the products of cracking processes. Several patents have disclosed the use of various additives as components in cracking catalysts to modify product distributions. U.S. Pat. No. 4,284,529 discloses the use of a catalyst additive comprising a zeolite having an alpha value not less than about 5 and having substantially no activity for cracking n-hexane. U.S. Pat. No. 4,239,654 discloses a catalyst composition comprising an ultrastable Y-type crystalline aluminosilicate zeolite, a catalytic inorganic oxide matrix and a small pore crystalline ZSM-type zeolite. U.S. Pat. No. 4,289,606 is similar to U.S. Pat. No. 4,239,654 in that a small pore crystalline ZSM-5 type zeolite is employed with an ultrastable Y-type crystalline aluminosilicate zeolite as the catalyst. U.S. Pat. Nos. 4,309,279 and 4,309,280 relate to the use of a zeolite additive to cracking processes wherein the zeolite is characterized by a Constraint Index of about 1 to 12 and a silica to alumina ratio greater than about 12. The above processes relate to the use of zeolite mixtures and are necessarily limited to zeolites.
U.S. Pat. No. 4,440,871 discloses a novel class of crystalline microporous silicoaluminophosphate molecular sieves. These silicoaluminophosphates are generally disclosed as being useful for various hydrocarbon conversion processes, including catalytic cracking processes. The use of the silicoaluminophosphates of U.S. Pat. No. 4,440,871 as components in conventional cracking catalysts for the conversion of crude oil feedstocks containing carbon-hydrogen fragmentation compounds is disclosed in copending U.S. Ser. No. 490,952, filed May 2, 1983. Although the above generally disclose the use of the silicoaluminophosphates in cracking processes such do not disclose the use of specific silicoaluminophosphates to provide improved product distribution, as hereinafter discussed.
The use of silicoaluminophosphate molecular sieves as cracking catalysts is disclosed in copending U.S. Ser. No. 675,279, filed concurrently herewith and commonly assigned.
The instant invention relates to the use of specific silicoaluminophosphate molecular sieves as components in cracking catalysts and to catalytic cracking processes. When such silicoaluminophosphate molecular sieves are added to cracking catalysts and employed in catalytic cracking processes such processes give products having product distributions substantially different and more valuable from that obtained in the absence of such silicoaluminophosphate molecular sieves.